In automobile collisions, it is common for a side mirror or other outside object to cause a tempered glass door window to fracture and then vacate the opening. Inertia can then cause a driver's or passenger's head or body to strike against the door window. In order to minimize injury resulting from a full or partial ejection, it is desirable to use window glass that deforms without shattering and vacating the opening, thereby absorbing impact and reducing the forces sustained by the passenger or driver. At the same time, it is important to mitigate full or partial ejection, that is, to prevent the head or other body parts from passing though the window opening in order to minimize the risk of injury and other serious consequences of full or partial ejection.
These problems have been addressed over many years by various improvements in automotive window glass. HPR (High Penetration Resistance) interlayer laminated glazing is a type of laminated glass introduced in the early 1960s, and is composed of a thin (e.g., 0.030 inch) layer of polyvinyl butyral (PVB) sandwiched between two layers of glass. The adhesion between the PVB layer and the glass layers is lower than the adhesion in earlier forms of laminated automotive glass, and the decreased adhesion has been found to increase penetration resistance significantly.
HPR glazing is now available in a heat-strengthened form, in which the two layers of glass used to form the PVB sandwich are tempered by thermal treatment.
Another form of HPR glazing is known as “advanced ejection mitigation glazing.” In this form of glazing, additional layers of PVB, and polyester films, similar to those used in so-called “Hurricane Glass” used in construction trades, are incorporated into the laminate in order to increase penetration resistance, and to maximize occupant containment.
Because most motor vehicle side windows in doors are designed to be opened by rolling them downward into a door frame, either manually or by the use of an electric motor, it is impossible to adhere the upper edge and the sides of the window to the door frame or window channel. Therefore, special measures need to be taken to prevent the window from moving out of the window channel in the door frame as a result of impact. In U.S. Pat. No. 4,823,511, for example, an automotive door window includes a retention shield in the form of a layer of PVB, polycarbonate resin, or acrylic resin, and an edge support molded onto peripheral vertical edge portions of the retention shield, in order to prevent the movable window assembly from releasing from the surrounding door frame when pressure is applied to the window. In U.S. Pat. Nos. 5,707,695 and 5,858,483, a channel is provided in the door frame. The door frame channel has flanges that prevent the laminated glass from dislodging from the channel during crash incidents.
A vehicle side window composed of HPR laminated glazing and advanced ejection mitigation laminated glazing is effective to mitigate ejection when it is fully rolled up and seated in the side window channels and upper window channel in the door frame. However, when the window is partly open, crash forces can cause the upper edge of the window to deform excessively, and pull the side edges out of their channels, so that, although the laminated glass provides containment superior to that of tempered glass, it does not meet its full potential as protection against full or partial ejection, and the risk of injury is increased.